Glycidyl tertiary carbonic ester is a highly branched glycidyl ester of α-branch monosaturated aliphatic acid (also referred to as glycidyl ester of branched carboxylic acid). The product can be used to prepare acrylic acid modified resins, polyester modified resins, alcohol acid modified resins and epoxy resins. It can also be used as active diluents for paints. It can significantly improve the properties of paints and is an important raw material for high-quality car paints, coil paints and metal paints.
Among the present technologies, the preparation of glycidylester of tertiary carbonic acid by the reaction between tertiary carbonic acid and halo substituted monoepoxides is mainly achieved by a two-step method, i.e. the first step is synthesis of intermediate product of halo substituted alcohol ester of tertiary carbonic acid, and the second step is conversion from the intermediate product into the final product glycidylester of tertiary carbonic acid.
For example, the glycidylester of tertiary carbonic acid could be directly prepared with carbonic acid and epoxy chloropropane, under catalysis of alkali metal hydroxide as well as dehydrochlorination, wherein glycidyl ester, alkali metal salt and water are produced. During this process, several high boiling point byproducts can be produced, with different yields, which may comprise halo substituted alcohol ester derivatives, derivatives produced by the reaction of halo substituted alcohol ester and epoxy chloropropane, and derivatives of glycidyl ester, presenting about 8%-12% of the total weight of the product. As the glycidylester of tertiary carbonic acid is easily deteriorated under heat or acidic or basic condition, therefore, the heating time for its purification by distillation is strictly limited. WO 97/44335 disclosed a method by which a product with a purity of 99% could be obtained. The product has a light color, and the color is stable during storage, but the product yield is relative low, 30% only, thus the cost is relatively high, and the industrial productive value is relatively low.
A method for the preparation of glycidyl esters of branched monocarboxylic acids was published in Chinese Patent CN99811327.1, wherein in the presence of water and a water-miscible solvent (isopropanol), catalyzed with catalyst (alkali metal hydroxide or alkali metal alkoxide), carboxylic acid reacts with halo substituted epoxides. Then by the dehydrohalogenation via the addition of base in two steps, glycidyl ester, alkali metal salt and water were produced. According to CN99811327.1, color-stable, during storage, glycidyl ester of branched monocarboxylic acids with very high level purity were obtained without distillation, and the content of high boiling point byproducts was lower than 6 wt %.
However, this method presents the following defects:
1. Water-miscible solvent is applied in the first step of catalytic synthesis. Large amount of water was required in this step (total amount of water is 4-13 times of the mole of carbonic acid). Due to the low concentration of saline water produced, it is unavoidable to bring some of the solvent, halo substituted epoxy propane and the product obtained into the diluted saline water while separating the saline water obtained during the first step, resulting in the loss of the solvent, halo substituted epoxy propane and the product. As for the recovery of organics in said diluted saline water, in one hand, raw materials and products would be lost due to incomplete recovery of solvent and thus poor recovery of halo substituted epoxy propane and products produced; in another hand, unrecovered halo substituted epoxy propane and products produced would become waste water or solid waste and then affect the environment.
2. Example 1 of CN99811327.1 shows that, large amount of isopropanol was used in the first step of catalytic synthesis, about 35% of the total reaction volume, which causes significant decrease of yield per unit volume. Therefore, this method is not suitable for industrial production. Meanwhile, side reactions between isopropanol and halo substituted epoxy propane will result undesired lost for halo substituted epoxy propane preparation.
3. Side reactions may occur during the first dehydrohalogenation by the addition of base because of the presence of halo substituted epoxy propane, resulting in the unnecessary loss of the halo substituted epoxy propane, thus reduced recovery rate of the raw material is decreased, which also causes increase of high boiling point byproducts, and the quality of the product is decreased.
4. The amount of epoxy chloropropane in the reaction was about 23% of the total reaction volume during the first dehydrohalogenation, which causes significant decrease of yield per unit volume. Therefore, this method is not suitable for industrial production.
5. While recovering halo substituted epoxy propane and solvent that is miscible with water by distillation, not only the recovery rate of the solvent and the halo substituted epoxy propane is reduced in the method because of the above reasons but also the solvent obtained is a mixed solvent, which is not suitable to be reused.
6. Second dehydrohalogenation is required for the method because the first dehydrohalogenation is not complete. The hydrolysis of the glycidyl ester is not avoidable during the second dehydrohalogenation. Thus the purity of the product is decreased, additional preparation procedures are required, and the preparation time is prolonged, so it is not suitable for industrial production.
In addition, a two-step synthesis method for glycidylester of tertiary carbonic acid was disclosed in Chinese patent CN200710056829.3. At first, the halo substituted alcohol ester of tertiary carbonic acid is produced by the reaction of carbonic acid and halo substituted epoxy propane under the catalysis of organic quaternary ammonium salt. Then glycidylester of tertiary carbonic acid, alkali metal salt and water are produced by the dehydrohalogenation via the addition of alkali metal hydroxide. Quaternary ammonium salt is used as a catalyst in this method, which also has some defects: at first, alkali metal hydroxides and alkali metal salts which are not solvable in the organic phase were brought into the organic phase by forming ion pair with tetra-alkyl ammonium ion via quaternary ammonium salt under action of lipophilic ammonium ion, resulting in the emulsification of the glycidyl ester; secondly, the organics can be brought into the aqueous phase by the charge effect of the lipophilic ammonium ion, causing the increase of the COD value of the waste water, thus resulted in more serious environmental pollution and loss of product. In order to solve the problems, the glycidylester of tertiary carbonic acid obtained by synthesis has to be separated and purified by distillation In this process, due to the heat-lability property of glycidylester of tertiary carbonic acid, decrease of the synthesis yield is unavoidable.
In conclusion, the method for preparing glycidylester of tertiary carbonic acid needs to be improved continuously, to improve the quality of the products, to decrease the cost and the influence to the environment and to be more suitable for industrial production.